The present invention is concerned generally with a thin and compact multi-layered optical system and method for generating well-organized output illumination from a spatially discontinuous one or two-dimensional array of discrete emitters, the output light emanating from one (or opposing sides) of the multi-layered system, uniformly over the system's aperture. The field of illumination produced by the optical systems containing these emitting arrays is rendered visually featureless so as to provide useful rear-illumination for an image to be viewed directly, an illuminating beam for an image to be projected onto a screen, or the illumination itself may be composed of an array of seamlessly arranged and controlled image pixels, the sum of which at any instant forming a spatially modulated image to be viewed directly. The field of even illumination so produced may also be used as a means of general illumination. More particularly, the multi-layer optical system that achieves this favorable performance uses a sequence of at least two optical light directing layers positioned relative to the emitting array surface or surfaces, these layers located at a preferred elevation above the discontinuously emitting source array, the layer constructions designed to even-out the light source array's brightness uniformity and color on the system's output aperture or output screen, and in doing so, form a uniform beam of light. An additional purpose of these precisely elevated optical layers is to establish a fixed angular range for the beam of emitted light. The system's first (and in some cases second) light manipulating layer is designed in such way that it shifts and expands the spatial distribution of input light so as to minimize brightness variations presented to subsequent layers and output screens. The related layer or layers, in configurations that need them, can be conventional light spreading materials such as holographic diffusers, lenticular diffusers, lens arrays, bulk or surface scattering diffusers, opal glass, or ground glass. The related layer or layers can also be a reflective polarizer that holds light of one polarization state within the light source structure until it converts to light of the orthogonal polarization. A base-diffusing layer, positioned just above the light source's emitting plane is added in some applications to introduce additional randomization.
Currently available illumination systems capable of achieving equivalent brightness uniformity using only conventional diffusers do so either less efficiently (in terms of brightness), in a thicker package, or both.
Such improved illumination systems are of primary interest for the projection of images onto screens from such spatial light modulators as reflective and transmissive LCDs and DMDs. Such improved illumination systems are also of interest for the backlighting of LCD screens, where illumination uniformity must be of extremely high quality without sacrificing any amount of brightness or compactness. LCD applications require the highest possible brightness combined with the thinnest possible packaging. Improved illumination systems are also of interest for backlighting passive appliqués used in a myriad of high brightness signage and display applications, including for example, one and two sided EXIT signs. Other applications for such improved illuminations systems include theatrical lighting, automotive headlights, safety warning lights, and certain traffic signals and alerts.
These improved illumination systems are also of interest for their intrinsic ability to display images directly, when the light source involved is made as a discontinuous array of individually-addressed light emitting regions or pixels whose boundaries are not contiguous, but when the multi-layer optical system achieves their seamless arrangement, so as to create an image characterized by both evenness of pixel illumination and maximization of pixel density.